Audio Output Balancing

ABSTRACT

An example implementation involves a first playback device receiving audio content to be played back by the first playback device and a second playback device in synchrony. Such audio content may include a first and second stereo component. The first playback device determines a limiting result that indicates frequencies at which a playback volume of the second playback device is limited and determines a crossover frequency based on the indicated frequencies at which the playback volume of the second playback device is limited. The first playback device causes the second playback device to play a first portion of the second stereo component that is above the determined crossover frequency and plays (i) the first stereo component and (ii) a second portion of the second stereo component that is below the indicated frequency in synchrony with playback of the first portion by the second playback device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 to, and is acontinuation of, U.S. non-provisional patent application Ser. No.14/937,523, filed on Nov. 10, 2015, entitled “Audio Output Balancing,”which is incorporated herein by reference. U.S. non-provisional patentapplication Ser. No. 14/937,523 claims priority under 35 U.S.C. §120 to,and is a continuation of, U.S. non-provisional patent application Ser.No. 14/174,253, filed on Feb. 6, 2014, entitled “Audio Output BalancingDuring Synchronized Playback,” and issued as U.S. Pat. No. 9,226,073 onDec. 29, 2015, which is also incorporated herein by reference.

FIELD OF THE DISCLOSURE

The disclosure is related to consumer goods and, more particularly, tomethods, systems, products, features, services, and other elementsdirected to media playback or some aspect thereof.

BACKGROUND

Options for accessing and listening to digital audio in an out-loudsetting were severely limited until in 2003, when SONOS, Inc. filed forone of its first patent applications, entitled “Method for SynchronizingAudio Playback between Multiple Networked Devices,” and began offering amedia playback system for sale in 2005. The Sonos Wireless HiFi Systemenables people to experience music from virtually unlimited sources viaone or more networked playback devices. Through a software controlapplication installed on a smartphone, tablet, or computer, one can playwhat he or she wants in any room that has a networked playback device.Additionally, using the controller, for example, different songs can bestreamed to each room with a playback device, rooms can be groupedtogether for synchronous playback, or the same song can be heard in allrooms synchronously.

Given the ever growing interest in digital media, there continues to bea need to develop consumer-accessible technologies to further enhancethe listening experience.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and advantages of the presently disclosed technologymay be better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 shows an example media playback system configuration in whichcertain embodiments may be practiced;

FIG. 2 shows a functional block diagram of an example playback device;

FIG. 3 shows a functional block diagram of an example control device;

FIG. 4 shows an example controller interface;

FIG. 5 shows a flow diagram of a first example method for audio outputbalancing during synchronized playback;

FIGS. 6A, 6B, 6C, and 6D show example synchronized playback audiosignals, example audio limiters, and example limited audio signals;

FIG. 7 shows a flow diagram of a second example method for audio outputbalancing during synchronized playback;

FIGS. 8A, 8B, 8C, and 8D show additional example synchronized playbackaudio signals, example audio limiters, and example limited audiosignals;

FIG. 9 shows a flow diagram of an example method for adjusting acrossover frequency for audio output balancing during synchronizedplayback; and

FIGS. 10A, 10B, 10C, 10D, 10E, and 10F show further example synchronizedplayback audio signals, example audio limiters, and example limitedaudio signals.

The drawings are for the purpose of illustrating example embodiments,but it is understood that the inventions are not limited to thearrangements and instrumentality shown in the drawings.

DETAILED DESCRIPTION I. Overview

Embodiments described herein involve balancing of outputs from playbackdevices playing audio content in synchrony. The playback devices may betwo or more playback devices of a media playback system that have beenconfigured as a synchrony group (two or more playback devices configuredto play audio content in synchrony), stereo paired playback devices, aconsolidated player, or any combination thereof. Discussions of examplemedia playback systems, example playback devices, and exampleconfigurations of playback devices of the media playback system may befound below in sections II.a.-II.d.

Typically, playback devices of the media system have acoustic limits.Acoustic limits of a playback device may be generally described as amaximum playback volume of the playback device before the acousticoutput quality of the playback device begins to deteriorate. Theacoustic limit of a playback device may vary over an audio playbackfrequency range of the playback device. In discussions herein, anacoustic limit of a playback device may also account for electric limitsor other operational limits of the playback device. Accordingly, alimiter may be implemented on the playback device to attenuate inputsignals above a playback volume threshold such that the output of theplayback device is capped at a certain volume level, thereby improvingthe acoustic output quality of the playback device. In one example, anamplifier gain control of the playback device may be implemented as thelimiter. In such a case, a gain value of the playback device may becapped such that an input signal is not amplified beyond the playbackvolume threshold of the playback device. The limiter may be a dynamiclimiter such that the gain value cap may be dynamically adjustedaccording to amplitudes of the input audio signal. Other example limiterimplementations may also be possible.

In one example configuration for audio content playback, two playbackdevices may be configured as a stereo pair. In one case, the playbackdevices of a stereo pair may have different acoustic limits, and maytherefore have different limiters implemented thereon. For instance, aleft channel playback device of the stereo pair may have a higherplayback volume threshold than a right channel playback device of thestereo pair. This may be, for example, because the left channel playbackdevice and the right channel playback device have different audioamplifier and/or different transducer configurations and specifications.As a result of the different limiters, the output volume from the leftchannel playback device and the right channel playback device may becomemismatched when a playback volume of the stereo pair is beyond theplayback volume threshold one of the respective playback devices. Insome cases, even if the left channel playback device and the rightchannel playback device have the same (or substantially the same) audioamplifier and transducer configurations and specifications (i.e. theplayback devices are the same production model), and therefore havingcomparable acoustic limits and limiters implemented thereon, the leftand right channel audio components of audio content to be rendered bythe stereo pair may be sufficiently mismatched in volume such that oneof the playback devices may still reach a limit before the otherplayback device.

In one example embodiment of the present application, the left channelplayback device of the two stereo paired playback devices may beconfigured to receive both the left channel audio component and theright channel audio component. In one case, the left channel playbackdevice may have access to the limiter for the right channel playbackdevice. As such, the left channel playback device may apply the limiterfor the right channel playback device to the right channel audiocomponent. The left channel playback device may then determine a limiterbased on a result of applying the right channel playback device limiterto the right channel audio component. In this case, the determinedlimiter may correlate to the acoustic limit of the right channelplayback device. As such, the left channel playback device may apply thedetermined limiter when playing the left channel audio component whilethe right channel playback device renders the right channel audiocomponent to achieve a balanced output from the stereo pair.

In another example audio content playback configuration, playbackdevices of a consolidated player may have different acoustic limits, andmay therefore have different limiters implemented thereon. In one case,the consolidated player may include a mid-high frequency range playbackdevice configured to render a mid-high frequency range audio component,and a low frequency range playback device (i.e. a subwoofer) configuredto render a low frequency audio component. The mid-high frequency rangeaudio component may have a first crossover frequency and the lowfrequency audio component may have a second crossover frequency. In somecases, the first and second crossover frequencies may be the samefrequency.

In this example, the low frequency range playback device may have ahigher acoustic limit than an acoustic limit of the mid-high frequencyrange playback device. Accordingly, the low frequency range playbackdevice may have a playback volume threshold higher than that of themid-high frequency range playback device. As a result of the differentlimiters, the low frequency output volume of the consolidated player andthe mid-high frequency output volume of the consolidated player maybecome mismatched when the playback volume of the consolidated player isbeyond the playback volume threshold of the mid-high frequency rangeplayback device.

In one example embodiment of the present application, one or more of theplayback devices of the consolidated player may receive a plurality ofaudio components, including audio components to be rendered by theplayback device as well as audio components to be rendered by adifferent playback device. As one example, the low frequency rangeplayback device may be configured to receive the low frequency audiocomponent to be rendered by the low frequency range playback device aswell as the mid-high frequency audio component to be rendered by themid-high frequency range playback device. In one case, the low frequencyrange playback device may have access to the limiter for the mid-highfrequency range playback device. As such, the low frequency rangeplayback device may apply the limiter for the mid-high frequency rangeplayback device to the mid-high frequency audio component to determine afirst limiting result, and apply the limiter for the low frequency rangeplayback device to the low frequency audio component to determine asecond limiting result. In one example, determining the first limitingresult may involve generating a model limited mid-high frequency audiosignal by applying the limiter for the mid-high frequency range playbackdevice to the mid-high frequency audio component. Similarly, determiningthe second limiting result may involve generating a model limited lowfrequency audio signal by applying the limiter for the low frequencyrange playback device to the low frequency audio component.

Based on the first and second limiting results, the low frequency rangeaudio playback device may determine a limiter to apply to the lowfrequency audio component when rendering the low frequency audiocomponent in synchrony with playback of the mid-high frequency audiocomponent by the mid-high frequency range playback device as aconsolidated player to achieve a balanced output across the audiofrequency spectrum.

In another example embodiment, the acoustic limit of the mid-highfrequency range playback device of a consolidated player may be lowertowards the lower end of the mid-high frequency playback range thanother playback frequency ranges of the mid-high frequency range playbackdevice. In other words, the acoustic limit towards the lower end of themid-high frequency playback range may become the limiting factor whenapplying the limiter of the mid-high frequency range playback device tothe mid-high frequency audio component.

In such a scenario, if the low-frequency range playback device of theconsolidated player is capable of playing frequencies in the lower endof the mid-high frequency playback range of the mid-high frequency rangeplayback device at a higher acoustic limit, the crossover frequency forplaying the low-frequency audio signal on the low-frequency rangeplayback device may be shifted to a higher frequency. Also, thecrossover frequency for playing the mid-high frequency audio signal onthe mid-high frequency range playback device may also be shifted to ahigher frequency. In other words, audio content within a frequency rangetowards the lower end of the mid-high frequency playback range may beplayed by the low frequency range playback device, rather than themid-high frequency range playback device. Accordingly, in some cases,applying the limiter for the mid-high frequency range playback device tothe modified mid-high frequency component may result in a less limitedplayback of the mid-high frequency audio component by the mid-highfrequency range playback device, and the balanced output of theconsolidated player may have a higher volume.

While the above example embodiments generally involve two playbackdevices as a either a stereo pair or consolidated player, one havingordinary in the art will appreciate that concepts within the exampleembodiments may be extended to any number of playback devices in a mediaplayback system configured as any one or more of a synchrony group,stereo paired playback devices, or a consolidated player. In addition,while the above example embodiments describe certain grouped players(e.g., a left player in a stereo pair or a low frequency-range playbackdevice in a consolidated player) performing various functions, it shouldbe understood that other players in the group could perform thesefunctions as well.

As indicated above, the present application involves balancing ofoutputs from playback devices playing audio content in synchrony. In oneaspect, a first playback device is provided. The first playback deviceincludes a processor, and memory having stored thereon instructionsexecutable by the processor to cause the first playback device toperform functions. The functions include receiving a first audio signal.The first playback device is configured to play the first audio signalaccording to a first crossover frequency. The functions also includedetermining a first limiting result by applying a limiting function to asecond audio signal. The second audio signal is configured for playbackby a second playback device according to a second crossover frequency,and the limiting function is associated with the second playback device.The functions further include, based on the first limiting result,configuring the first playback device to play the first audio signalaccording to a third crossover frequency.

In another aspect, a method is provided. The method involves receiving,by a first playback device, audio content comprising a first audiosignal and a second audio signal. The first playback device isconfigured to play the first audio signal according to a first crossoverfrequency in synchrony with the playback of the second audio signalaccording to a second crossover frequency by a second playback device.The method also involves determining a first limiting result byapplying, by the first playback device, a first limiting function to thefirst audio signal. The first limiting function is associated with thefirst playback device. The method further involves determining a secondlimiting result by applying, by the first playback device, a secondlimiting function to the second audio signal. The second limitingfunction is associated with the second playback device. The method alsoinvolves, based on the first limiting result and the second limitingresult, configuring the first playback device to play the first audiosignal according to a third crossover frequency.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform functions. The functions include receiving a firstaudio signal. The first playback device is configured to play the firstaudio signal according to a first crossover frequency. The functionsalso include determining a first limiting result by applying a limitingfunction to a second audio signal. The second audio signal is configuredfor playback by a second playback device according to a second crossoverfrequency, and the limiting function is associated with the secondplayback device. The functions further include, based on the firstlimiting result, configuring the first playback device to play the firstaudio signal according to a third crossover frequency.

It will be understood by one of ordinary skill in the art that thisdisclosure includes numerous other embodiments.

II. Example Operating Environment

FIG. 1 shows an example configuration of a media playback system 100 inwhich one or more embodiments disclosed herein may be practiced orimplemented. The media playback system 100 as shown is associated withan example home environment having several rooms and spaces, such as forexample, a master bedroom, an office, a dining room, and a living room.As shown in the example of FIG. 1, the media playback system 100includes playback devices 102-124, control devices 126 and 128, and awired or wireless network router 130.

Further discussions relating to the different components of the examplemedia playback system 100 and how the different components may interactto provide a user with a media experience may be found in the followingsections. While discussions herein may generally refer to the examplemedia playback system 100, technologies described herein are not limitedto applications within, among other things, the home environment asshown in FIG. 1. For instance, the technologies described herein may beuseful in environments where multi-zone audio may be desired, such as,for example, a commercial setting like a restaurant, mall or airport, avehicle like a sports utility vehicle (SUV), bus or car, a ship or boat,an airplane, and so on.

a. Example Playback Devices

FIG. 2 shows a functional block diagram of an example playback device200 that may be configured to be one or more of the playback devices102-124 of the media playback system 100 of FIG. 1. The playback device200 may include a processor 202, software components 204, memory 206,audio processing components 208, audio amplifier(s) 210, speaker(s) 212,and a network interface 214 including wireless interface(s) 216 andwired interface(s) 218. In one case, the playback device 200 may notinclude the speaker(s) 212, but rather a speaker interface forconnecting the playback device 200 to external speakers. In anothercase, the playback device 200 may include neither the speaker(s) 212 northe audio amplifier(s) 210, but rather an audio interface for connectingthe playback device 200 to an external audio amplifier or audio-visualreceiver.

In one example, the processor 202 may be a clock-driven computingcomponent configured to process input data according to instructionsstored in the memory 206. The memory 206 may be a tangiblecomputer-readable medium configured to store instructions executable bythe processor 202. For instance, the memory 206 may be data storage thatcan be loaded with one or more of the software components 204 executableby the processor 202 to achieve certain functions. In one example, thefunctions may involve the playback device 200 retrieving audio data froman audio source or another playback device. In another example, thefunctions may involve the playback device 200 sending audio data toanother device or playback device on a network. In yet another example,the functions may involve pairing of the playback device 200 with one ormore playback devices to create a multi-channel audio environment.

Certain functions may involve the playback device 200 synchronizingplayback of audio content with one or more other playback devices.During synchronous playback, a listener will preferably not be able toperceive time-delay differences between playback of the audio content bythe playback device 200 and the one or more other playback devices. U.S.Pat. No. 8,234,395 entitled, “System and method for synchronizingoperations among a plurality of independently clocked digital dataprocessing devices,” which is hereby incorporated by reference, providesin more detail some examples for audio playback synchronization amongplayback devices.

The memory 206 may further be configured to store data associated withthe playback device 200, such as one or more zones and/or zone groupsthe playback device 200 is a part of, audio sources accessible by theplayback device 200, or a playback queue that the playback device 200(or some other playback device) may be associated with. The data may bestored as one or more state variables that are periodically updated andused to describe the state of the playback device 200. The memory 206may also include the data associated with the state of the other devicesof the media system, and shared from time to time among the devices sothat one or more of the devices have the most recent data associatedwith the system. Other embodiments are also possible.

The audio processing components 208 may include one or moredigital-to-analog converters (DAC), an audio preprocessing component, anaudio enhancement component or a digital signal processor (DSP), and soon. In one embodiment, one or more of the audio processing components208 may be a subcomponent of the processor 202. In one example, audiocontent may be processed and/or intentionally altered by the audioprocessing components 208 to produce audio signals. The produced audiosignals may then be provided to the audio amplifier(s) 210 foramplification and playback through speaker(s) 212. Particularly, theaudio amplifier(s) 210 may include devices configured to amplify audiosignals to a level for driving one or more of the speakers 212. Thespeaker(s) 212 may include an individual transducer (e.g., a “driver”)or a complete speaker system involving an enclosure with one or moredrivers. A particular driver of the speaker(s) 212 may include, forexample, a subwoofer (e.g., for low frequencies), a mid-range driver(e.g., for middle frequencies), and/or a tweeter (e.g., for highfrequencies). In some cases, each transducer in the one or more speakers212 may be driven by an individual corresponding audio amplifier of theaudio amplifier(s) 210. In addition to producing analog signals forplayback by the playback device 200, the audio processing components 208may be configured to process audio content to be sent to one or moreother playback devices for playback.

Audio content to be processed and/or played back by the playback device200 may be received from an external source, such as via an audioline-in input connection (e.g., an auto-detecting 3.5 mm audio line-inconnection) or the network interface 214.

The network interface 214 may be configured to facilitate a data flowbetween the playback device 200 and one or more other devices on a datanetwork. As such, the playback device 200 may be configured to receiveaudio content over the data network from one or more other playbackdevices in communication with the playback device 200, network deviceswithin a local area network, or audio content sources over a wide areanetwork such as the Internet. In one example, the audio content andother signals transmitted and received by the playback device 200 may betransmitted in the form of digital packet data containing an InternetProtocol (IP)-based source address and IP-based destination addresses.In such a case, the network interface 214 may be configured to parse thedigital packet data such that the data destined for the playback device200 is properly received and processed by the playback device 200.

As shown, the network interface 214 may include wireless interface(s)216 and wired interface(s) 218. The wireless interface(s) 216 mayprovide network interface functions for the playback device 200 towirelessly communicate with other devices (e.g., other playbackdevice(s), speaker(s), receiver(s), network device(s), control device(s)within a data network the playback device 200 is associated with) inaccordance with a communication protocol (e.g., any wireless standardincluding IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4Gmobile communication standard, and so on). The wired interface(s) 218may provide network interface functions for the playback device 200 tocommunicate over a wired connection with other devices in accordancewith a communication protocol (e.g., IEEE 802.3). While the networkinterface 214 shown in FIG. 2 includes both wireless interface(s) 216and wired interface(s) 218, the network interface 214 may in someembodiments include only wireless interface(s) or only wiredinterface(s).

In one example, the playback device 200 and one other playback devicemay be paired to play two separate audio components of audio content.For instance, playback device 200 may be configured to play a leftchannel audio component, while the other playback device may beconfigured to play a right channel audio component, thereby producing orenhancing a stereo effect of the audio content. The paired playbackdevices (also referred to as “bonded playback devices”) may further playaudio content in synchrony with other playback devices.

In another example, the playback device 200 may be sonicallyconsolidated with one or more other playback devices to form a single,consolidated playback device. A consolidated playback device may beconfigured to process and reproduce sound differently than anunconsolidated playback device or playback devices that are paired,because a consolidated playback device may have additional speakerdrivers through which audio content may be rendered. For instance, ifthe playback device 200 is a playback device designed to render lowfrequency range audio content (i.e. a subwoofer), the playback device200 may be consolidated with a playback device designed to render fullfrequency range audio content. In such a case, the full frequency rangeplayback device, when consolidated with the low frequency playbackdevice 200, may be configured to render only the mid and high frequencycomponents of audio content, while the low frequency range playbackdevice 200 renders the low frequency component of the audio content. Theconsolidated playback device may further be paired with a singleplayback device or yet another consolidated playback device.

By way of illustration, SONOS, Inc. presently offers (or has offered)for sale certain playback devices including a “PLAY:1,” “PLAY:3,”“PLAY:5,” “PLAYBAR,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Any otherpast, present, and/or future playback devices may additionally oralternatively be used to implement the playback devices of exampleembodiments disclosed herein. Additionally, it is understood that aplayback device is not limited to the example illustrated in FIG. 2 orto the SONOS product offerings. For example, a playback device mayinclude a wired or wireless headphone. In another example, a playbackdevice may include or interact with a docking station for personalmobile media playback devices. In yet another example, a playback devicemay be integral to another device or component such as a television, alighting fixture, or some other device for indoor or outdoor use.

b. Example Playback Zone Configurations

Referring back to the media playback system 100 of FIG. 1, theenvironment may have one or more playback zones, each with one or moreplayback devices. The media playback system 100 may be established withone or more playback zones, after which one or more zones may be added,or removed to arrive at the example configuration shown in FIG. 1. Eachzone may be given a name according to a different room or space such asan office, bathroom, master bedroom, bedroom, kitchen, dining room,living room, and/or balcony. In one case, a single playback zone mayinclude multiple rooms or spaces. In another case, a single room orspace may include multiple playback zones.

As shown in FIG. 1, the balcony, dining room, kitchen, bathroom, office,and bedroom zones each have one playback device, while the living roomand master bedroom zones each have multiple playback devices. In theliving room zone, playback devices 104, 106, 108, and 110 may beconfigured to play audio content in synchrony as individual playbackdevices, as one or more bonded playback devices, as one or moreconsolidated playback devices, or any combination thereof. Similarly, inthe case of the master bedroom, playback devices 122 and 124 may beconfigured to play audio content in synchrony as individual playbackdevices, as a bonded playback device, or as a consolidated playbackdevice.

In one example, one or more playback zones in the environment of FIG. 1may each be playing different audio content. For instance, the user maybe grilling in the balcony zone and listening to hip hop music beingplayed by the playback device 102 while another user may be preparingfood in the kitchen zone and listening to classical music being playedby the playback device 114. In another example, a playback zone may playthe same audio content in synchrony with another playback zone. Forinstance, the user may be in the office zone where the playback device118 is playing the same rock music that is being playing by playbackdevice 102 in the balcony zone. In such a case, playback devices 102 and118 may be playing the rock music in synchrony such that the user mayseamlessly (or at least substantially seamlessly) enjoy the audiocontent that is being played out-loud while moving between differentplayback zones. Synchronization among playback zones may be achieved ina manner similar to that of synchronization among playback devices, asdescribed in previously referenced U.S. Pat. No. 8,234,395.

As suggested above, the zone configurations of the media playback system100 may be dynamically modified, and in some embodiments, the mediaplayback system 100 supports numerous configurations. For instance, if auser physically moves one or more playback devices to or from a zone,the media playback system 100 may be reconfigured to accommodate thechange(s). For instance, if the user physically moves the playbackdevice 102 from the balcony zone to the office zone, the office zone maynow include both the playback device 118 and the playback device 102.The playback device 102 may be paired or grouped with the office zoneand/or renamed if so desired via a control device such as the controldevices 126 and 128. On the other hand, if the one or more playbackdevices are moved to a particular area in the home environment that isnot already a playback zone, a new playback zone may be created for theparticular area.

Further, different playback zones of the media playback system 100 maybe dynamically combined into zone groups or split up into individualplayback zones. For instance, the dining room zone and the kitchen zone114 may be combined into a zone group for a dinner party such thatplayback devices 112 and 114 may render audio content in synchrony. Onthe other hand, the living room zone may be split into a television zoneincluding playback device 104, and a listening zone including playbackdevices 106, 108, and 110, if the user wishes to listen to music in theliving room space while another user wishes to watch television.

c. Example Control Devices

FIG. 3 shows a functional block diagram of an example control device 300that may be configured to be one or both of the control devices 126 and128 of the media playback system 100. As shown, the control device 300may include a processor 302, memory 304, a network interface 306, and auser interface 308. In one example, the control device 300 may be adedicated controller for the media playback system 100. In anotherexample, the control device 300 may be a network device on which mediaplayback system controller application software may be installed, suchas for example, an iPhone™, iPad™ or any other smart phone, tablet ornetwork device (e.g., a networked computer such as a PC or Mac™).

The processor 302 may be configured to perform functions relevant tofacilitating user access, control, and configuration of the mediaplayback system 100. The memory 304 may be configured to storeinstructions executable by the processor 302 to perform those functions.The memory 304 may also be configured to store the media playback systemcontroller application software and other data associated with the mediaplayback system 100 and the user.

In one example, the network interface 306 may be based on an industrystandard (e.g., infrared, radio, wired standards including IEEE 802.3,wireless standards including IEEE 802.11a, 802.11b, 802.11g, 802.11n,802.11ac, 802.15, 4G mobile communication standard, and so on). Thenetwork interface 306 may provide a means for the control device 300 tocommunicate with other devices in the media playback system 100. In oneexample, data and information (e.g., such as a state variable) may becommunicated between control device 300 and other devices via thenetwork interface 306. For instance, playback zone and zone groupconfigurations in the media playback system 100 may be received by thecontrol device 300 from a playback device or another network device, ortransmitted by the control device 300 to another playback device ornetwork device via the network interface 306. In some cases, the othernetwork device may be another control device.

Playback device control commands such as volume control and audioplayback control may also be communicated from the control device 300 toa playback device via the network interface 306. As suggested above,changes to configurations of the media playback system 100 may also beperformed by a user using the control device 300. The configurationchanges may include adding/removing one or more playback devices to/froma zone, adding/removing one or more zones to/from a zone group, forminga bonded or consolidated player, separating one or more playback devicesfrom a bonded or consolidated player, among others. Accordingly, thecontrol device 300 may sometimes be referred to as a controller, whetherthe control device 300 is a dedicated controller or a network device onwhich media playback system controller application software isinstalled.

The user interface 308 of the control device 300 may be configured tofacilitate user access and control of the media playback system 100, byproviding a controller interface such as the controller interface 400shown in FIG. 4. The controller interface 400 includes a playbackcontrol region 410, a playback zone region 420, a playback status region430, a playback queue region 440, and an audio content sources region450. The user interface 400 as shown is just one example of a userinterface that may be provided on a network device such as the controldevice 300 of FIG. 3 (and/or the control devices 126 and 128 of FIG. 1)and accessed by users to control a media playback system such as themedia playback system 100. Other user interfaces of varying formats,styles, and interactive sequences may alternatively be implemented onone or more network devices to provide comparable control access to amedia playback system.

The playback control region 410 may include selectable (e.g., by way oftouch or by using a cursor) icons to cause playback devices in aselected playback zone or zone group to play or pause, fast forward,rewind, skip to next, skip to previous, enter/exit shuffle mode,enter/exit repeat mode, enter/exit cross fade mode. The playback controlregion 410 may also include selectable icons to modify equalizationsettings, and playback volume, among other possibilities.

The playback zone region 420 may include representations of playbackzones within the media playback system 100. In some embodiments, thegraphical representations of playback zones may be selectable to bringup additional selectable icons to manage or configure the playback zonesin the media playback system, such as a creation of bonded zones,creation of zone groups, separation of zone groups, and renaming of zonegroups, among other possibilities.

For example, as shown, a “group” icon may be provided within each of thegraphical representations of playback zones. The “group” icon providedwithin a graphical representation of a particular zone may be selectableto bring up options to select one or more other zones in the mediaplayback system to be grouped with the particular zone. Once grouped,playback devices in the zones that have been grouped with the particularzone will be configured to play audio content in synchrony with theplayback device(s) in the particular zone. Analogously, a “group” iconmay be provided within a graphical representation of a zone group. Inthis case, the “group” icon may be selectable to bring up options todeselect one or more zones in the zone group to be removed from the zonegroup. Other interactions and implementations for grouping andungrouping zones via a user interface such as the user interface 400 arealso possible. The representations of playback zones in the playbackzone region 420 may be dynamically updated as playback zone or zonegroup configurations are modified.

The playback status region 430 may include graphical representations ofaudio content that is presently being played, previously played, orscheduled to play next in the selected playback zone or zone group. Theselected playback zone or zone group may be visually distinguished onthe user interface, such as within the playback zone region 420 and/orthe playback status region 430. The graphical representations mayinclude track title, artist name, album name, album year, track length,and other relevant information that may be useful for the user to knowwhen controlling the media playback system via the user interface 400.

The playback queue region 440 may include graphical representations ofaudio content in a playback queue associated with the selected playbackzone or zone group. In some embodiments, each playback zone or zonegroup may be associated with a playback queue containing informationcorresponding to zero or more audio items for playback by the playbackzone or zone group. For instance, each audio item in the playback queuemay comprise a uniform resource identifier (URI), a uniform resourcelocator (URL) or some other identifier that may be used by a playbackdevice in the playback zone or zone group to find and/or retrieve theaudio item from a local audio content source or a networked audiocontent source, possibly for playback by the playback device.

In one example, a playlist may be added to a playback queue, in whichcase information corresponding to each audio item in the playlist may beadded to the playback queue. In another example, audio items in aplayback queue may be saved as a playlist. In a further example, aplayback queue may be empty, or populated but “not in use” when theplayback zone or zone group is playing continuously streaming audiocontent, such as Internet radio that may continue to play untilotherwise stopped, rather than discrete audio items that have playbackdurations. In an alternative embodiment, a playback queue can includeInternet radio and/or other streaming audio content items and be “inuse” when the playback zone or zone group is playing those items. Otherexamples are also possible.

When playback zones or zone groups are “grouped” or “ungrouped,”playback queues associated with the affected playback zones or zonegroups may be cleared or re-associated. For example, if a first playbackzone including a first playback queue is grouped with a second playbackzone including a second playback queue, the established zone group mayhave an associated playback queue that is initially empty, that containsaudio items from the first playback queue (such as if the secondplayback zone was added to the first playback zone), that contains audioitems from the second playback queue (such as if the first playback zonewas added to the second playback zone), or a combination of audio itemsfrom both the first and second playback queues. Subsequently, if theestablished zone group is ungrouped, the resulting first playback zonemay be re-associated with the previous first playback queue, or beassociated with a new playback queue that is empty or contains audioitems from the playback queue associated with the established zone groupbefore the established zone group was ungrouped. Similarly, theresulting second playback zone may be re-associated with the previoussecond playback queue, or be associated with a new playback queue thatis empty, or contains audio items from the playback queue associatedwith the established zone group before the established zone group wasungrouped. Other examples are also possible.

Referring back to the user interface 400 of FIG. 4, the graphicalrepresentations of audio content in the playback queue region 440 mayinclude track titles, artist names, track lengths, and other relevantinformation associated with the audio content in the playback queue. Inone example, graphical representations of audio content may beselectable to bring up additional selectable icons to manage and/ormanipulate the playback queue and/or audio content represented in theplayback queue. For instance, a represented audio content may be removedfrom the playback queue, moved to a different position within theplayback queue, or selected to be played immediately, or after anycurrently playing audio content, among other possibilities. A playbackqueue associated with a playback zone or zone group may be stored in amemory on one or more playback devices in the playback zone or zonegroup, on a playback device that is not in the playback zone or zonegroup, and/or some other designated device.

The audio content sources region 450 may include graphicalrepresentations of selectable audio content sources from which audiocontent may be retrieved and played by the selected playback zone orzone group. Discussions pertaining to audio content sources may be foundin the following section.

d. Example Audio Content Sources

As indicated previously, one or more playback devices in a zone or zonegroup may be configured to retrieve for playback audio content (e.g.according to a corresponding URI or URL for the audio content) from avariety of available audio content sources. In one example, audiocontent may be retrieved by a playback device directly from acorresponding audio content source (e.g., a line-in connection). Inanother example, audio content may be provided to a playback device overa network via one or more other playback devices or network devices.

Example audio content sources may include a memory of one or moreplayback devices in a media playback system such as the media playbacksystem 100 of FIG. 1, local music libraries on one or more networkdevices (such as a control device, a network-enabled personal computer,or a networked-attached storage (NAS), for example), streaming audioservices providing audio content via the Internet (e.g., the cloud), oraudio sources connected to the media playback system via a line-in inputconnection on a playback device or network devise, among otherpossibilities.

In some embodiments, audio content sources may be regularly added orremoved from a media playback system such as the media playback system100 of FIG. 1. In one example, an indexing of audio items may beperformed whenever one or more audio content sources are added, removedor updated. Indexing of audio items may involve scanning foridentifiable audio items in all folders/directory shared over a networkaccessible by playback devices in the media playback system, andgenerating or updating an audio content database containing metadata(e.g., title, artist, album, track length, among others) and otherassociated information, such as a URI or URL for each identifiable audioitem found. Other examples for managing and maintaining audio contentsources may also be possible.

The above discussions relating to playback devices, controller devices,playback zone configurations, and media content sources provide onlysome examples of operating environments within which functions andmethods described below may be implemented. Other operating environmentsand configurations of media playback systems, playback devices, andnetwork devices not explicitly described herein may also be applicableand suitable for implementation of the functions and methods.

III. Example Methods for Audio Output Balancing During SynchronizedPlayback

As discussed above, embodiments described herein may involve balancingof outputs from playback devices playing audio content in synchrony.

a. First Example Method for Audio Output Balancing During SynchronizedPlayback

FIG. 5 shows a flow diagram of a first example method for audio outputbalancing during synchronized playback. Method 500 shown in FIG. 5presents an embodiment of a method that can be implemented within anoperating environment involving, for example, the media playback system100 of FIG. 1, one or more of the playback device 200 of FIG. 2, and oneor more of the control device 300 of FIG. 3. Method 500 may include oneor more operations, functions, or actions as illustrated by one or moreof blocks 502-508. Although the blocks are illustrated in sequentialorder, these blocks may also be performed in parallel, and/or in adifferent order than those described herein. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or removed based upon the desired implementation.

In addition, for the method 500 and other processes and methodsdisclosed herein, the flowchart shows functionality and operation of onepossible implementation of present embodiments. In this regard, eachblock may represent a module, a segment, or a portion of program code,which includes one or more instructions executable by a processor forimplementing specific logical functions or steps in the process. Theprogram code may be stored on any type of computer readable medium, forexample, such as a storage device including a disk or hard drive. Thecomputer readable medium may include non-transitory computer readablemedium, for example, such as computer-readable media that stores datafor short periods of time like register memory, processor cache andRandom Access Memory (RAM). The computer readable medium may alsoinclude non-transitory media, such as secondary or persistent long termstorage, like read only memory (ROM), optical or magnetic disks,compact-disc read only memory (CD-ROM), for example. The computerreadable media may also be any other volatile or non-volatile storagesystems. The computer readable medium may be considered a computerreadable storage medium, for example, or a tangible storage device. Inaddition, for the method 500 and other processes and methods disclosedherein, each block in FIG. 5 may represent circuitry that is wired toperform the specific logical functions in the process.

At block 502, the method 500 involves receiving a first audio signal tobe played by a first playback device. In one example, the first playbackdevice may be configured to play the first audio signal in synchronywith the playback of a second audio signal by a second playback device.FIG. 6A shows a first example pair of synchronized playback audiosignals 602 and 604. In this example, audio signal 602 may be the firstaudio signal and may include audio content within a first examplefrequency range of approximately 20 Hz to 80 Hz. As such, a crossoverfrequency for audio signal 602 may be 80 Hz. Audio signal 604 may be thesecond audio signal and may include audio content with a second examplefrequency range of approximately 80 Hz to 20 kHz. In this example, audiosignal 602 may also have a crossover frequency of 80 Hz.

In this case, the first and second playback devices may be configured asa consolidated player, and the audio signal 602 may be the first audiosignal to be played by the first playback device while the audio signal604 may be the second audio signal to be played by the second playbackdevice. In such a case, the first playback device may be a playbackdevice configured for playing low frequency audio content (i.e., asubwoofer), and the second playback device may be a playback deviceconfigured to play a full frequency range or mid-high frequency range ofaudio content. For purposes of illustration, the first and secondplayback devices may be playback devices 104 and 110, respectively, asshown in FIG. 1.

FIG. 6B shows a second example pair of synchronized playback audiosignals 606 and 608. In this example, audio signal 608 may be the firstaudio signal and may include left channel components of a stereo audiocontent, while audio signal 606 may be the second audio signal and mayinclude right channel components of the stereo audio content. In thiscase, the first and second playback devices may be configured as astereo pair such that the first playback device is configured as a leftchannel speaker for playing the audio signal 608 while the secondplayback device is configured as a right channel speaker for playing theaudio signal 606. For purposes of illustration, the first and secondplayback devices in this case may be the playback devices 124 and 122,respectively, as shown in FIG. 1.

In one case, the first playback device in the consolidated player orstereo pair may be a primary player configured to receive audio signalsand send the audio signals to other playback devices within theconsolidated player or stereo pair for playback. As such, in oneexample, the first audio signal and the second audio signal may bereceived by the first playback device. For instance, in connection withFIG. 6A, the audio signals 602 and 604 may be received by a lowfrequency range playback device of the consolidated player, and inconnection with FIG. 6B, the audio signals 606 and 608 may be receivedby the left channel speaker of the stereo pair. In another case, thefirst playback device may be just any playback device in theconsolidated player or stereo pair. In some instances, each playbackdevice in the consolidated player or stereo pair may receive, eitherdirectly from a content source, from the primary player, or from someother source, the audio signals (or components of the audio signals) tobe rendered by the consolidated player or stereo pair.

Referring back to FIG. 5, block 504 of the method 500 involvesdetermining a first limiting result by applying to a second audio signala limiting function associated with a second playback device. Asindicated above, the second playback device may be a full or mid-highfrequency range playback device in the example in connection with FIG.6A, or a right channel speaker in the example in connection with FIG.6B. As previously indicated, the limiting function associated with thesecond playback device may represent an acoustic limit of the secondplayback device. As such, when applying the limiting function associatedwith the second playback to the second audio signal, the first playbackdevice generates a model of an audio signal that may be rendered by thesecond playback device when the second playback device plays the secondaudio signal.

The first playback device, in order to apply the limiting functionassociated with the second playback device, has access to the limitingfunction associated with the second playback device. In one example, thefirst playback device may receive the limiting function associated withthe second playback device when the consolidated player or stereo pairis formed. In another example, the first playback device may receive thelimiting function associated with the second playback device when eitherthe first playback device or the second playback device joins the mediaplayback system that the first and second playback devices are parts ofIn one case, the limiting function associated with the second playbackdevice may be provided to the first playback device by the secondplayback device. In another case, the limiting function associated withthe second playback device may be provided from a local or remotenetwork device or server.

In some instances, the limiting function associated with the secondplayback device may be specific to the particular second playbackdevice. In other instances, the limiting function associated with thesecond playback device may be associated with a production model of thesecond playback device, such that all playback devices of thatproduction model have the same limiting functions. In such instances,the first playback device may already have stored thereon a particularlimiting function associated with the production model of the secondplayback device and may access the particular limiting function as thelimiting function associated with the second playback device.

In some cases, the limiting function associated with the second playbackdevice may be a modified version of the limiting function that thesecond playback device actually applies when playing audio content. Forinstance, the limiting function applied by the first playback device maybe a simplified version of the limiting function applied by the secondplayback device when the second playback device is playing audio contentto lessen the processing load of the first playback device whenexecuting the block 504. Other examples of limiting functions andlimiting function sources are also possible.

For purposes of illustration, FIG. 6C shows an example application of alimiting function 650 to the second audio signal 606 discussedpreviously in connection to the example of FIG. 6B. In this example, thelimiting function 650 may be the limiting function associated with thesecond playback device, which as discussed above may be the rightchannel speaker of the stereo pair. As shown, applying the limitingfunction 650 results in a limited second audio signal 606′ that is aproportionally scaled down version of the second audio signal 606 suchthat the limited second audio signal 606′ is within the acoustic limitof the second playback device as defined by the limiting function 650,across the entire frequency range of the second audio signal 606. Asshown in this illustrative example, the first limiting result mayindicate that the limited second audio signal 606′ is the second audiosignal 606 scaled down by a ratio of b/(a+b).

In some cases, the acoustic limit of a playback device may be lower(more limited) towards the lower frequencies of the playback frequencyof the playback device. In other words, the ratio by which an audiosignal is scaled when applying the limiting function associated with theplayback device may be dependent primarily on the lower frequencies ofthe audio signal. In fact, in some instance, the limiting function mayonly be provided for lower frequency audio signal anyway. As such, thefirst playback device may in some embodiments, process the second audiosignal such that only the lower frequencies of the second audio signalremain (i.e. using a low-pass filter). Continuing with the examplesabove, the first playback device may consequently apply the limitingfunction 650 associated with the second playback device to just theremaining lower frequencies of the second audio signal 606 to determinethe first limiting result. In some cases, applying the limiting function650 to only the lower frequencies of the second audio signal 606 mayreduce the overall processing power and processing time of block 504.

For a balanced output between the playback of the first audio signal 608by the first playback device and playback of the second audio signal 606by the second playback device, the first audio signal 608 may need to belimited or proportionally scaled to match that of the limited secondaudio signal 606′ when played by the first playback device. Accordingly,at block 506, the method 500 involves determining a limiting functionbased on the first limiting result. FIG. 6D shows an example limitingfunction 660 determined based on the first limiting result discussedabove. As shown, the limiting function 660, when applied, may beconfigured to scale the first audio signal 608 by a ratio of d/(c+d). Inthis case, for a balanced output between the playback of the first audiosignal 608 and the second audio signal 606, d/(c+d)=b/(a+b).

At block 508, the method 500 involves configuring the first playbackdevice to apply the determined limiting function when playing the firstaudio signal. Referring to FIG. 6D again, the first playback device maybe configured to apply the limiting function 660 when playing the firstaudio signal 608. As shown, a limited first audio signal 608′ may begenerated when applying the limiting function 660 to the first audiosignal 608. The limited first audio signal 608′ is proportionally scaleddown from the first audio signal 608 by the ratio of d/(c+d). In oneexample, configuring the first playback device to apply the limitingfunction 660 to the first audio signal 608 may involve adjusting anamplifier gain applied to the first audio signal 608 by the firstplayback device. In one case, the amplifier gain may be adjusted to bed/(c+d) of unity gain. As also shown in FIG. 6D, the limited first audiosignal 608′ and the limited second audio signal 606′ are substantiallyas proportionally balanced as the first audio signal 608 and secondaudio signal 606 shown in FIG. 6B. Accordingly, when configured to applythe determined limiting function 660, the first playback device mayeffectively render the limited first audio signal 608′ when playing thefirst audio signal 608. In another example, applying the limitingfunction 660 to the first audio signal 608 may involve simply capping orclipping the first audio signal 608 according to the limiting function660, rather than proportionally scaling the first audio signal 608.

In one example, as suggested previously, the first playback device maybe a primary playback device in the stereo pair and as such may also beconfigured to cause and/or coordinate the second playback device to playthe second audio signal 606 in synchrony with the playback of the firstaudio signal 608. In some embodiments, synchronous playback between thefirst and second playback devices may be performed as described inpreviously referenced U.S. Pat. No. 8,234,395, also assigned to SONOS,Inc.

As a primary player, the first playback device may be configured to sendthe second audio signal 606 to the second playback device for the secondplayback device to play in synchrony with the playback of the firstaudio signal 608 by the first playback device (while applying thedetermined limiting function 660). In some embodiments, if the firstplayback device generated the limited second audio signal 606′ whenapplying the limiting function 650 to the second audio signal 606 todetermine the first limiting result in block 504, the first playbackdevice may send the limited second audio signal 606′ to the secondplayback device for the second playback device to render, therebyeliminating the need for the second playback device to apply thelimiting function 650 associated with the second device when playing thesecond audio signal 606. In other embodiments, the first playback devicemay simply send the audio signal 606 to the second playback device, andthe playback device may apply its limiting function 650 to the audiosignal 606.

While discussions above relating to the method 500 are generallydirected to the balancing of audio output during synchronized playbackby a stereo pair, one having ordinary skill in the art will appreciatethat method 500 may be applied to other synchronized playback scenariosas well. Further, note that in some embodiments, the illustrativeexamples discussed in connection to the method 500 and FIG. 6A-6Drepresent only one instance of a dynamic balancing of audio outputduring synchronized playback. In other words, method 500 may beperformed for each data packet or series of data packets containingaudio signals received as part of a streaming audio content.

b. Second Example Method for Audio Output Balancing During SynchronizedPlayback

In the example discussed above in connection to FIG. 5, the firstplayback device determines a limiting function for the first audiosignal to be played by the first device based on the result of applyingthe limiting function associated with the second playback device to thesecond audio signal to be played by the second device. This may be thecase when the first playback device and the second playback device havesimilar or comparable acoustic limits, or if the first playback devicehas a higher acoustic limit than the second playback device. In somecases, however, the limiting function for the first audio signal may bedetermined based on the result of applying the limiting functionassociated with the second playback device on the second audio signal aswell as a result of applying the limiting function associated with thefirst playback device on the first audio signal.

FIG. 7 shows a flow diagram of a second example method 700 for audiooutput balancing during synchronized playback. Method 700 shown in FIG.7 presents an embodiment of a method that can be implemented within anoperating environment involving, for example, the media playback system100 of FIG. 1, one or more of the playback device 200 of FIG. 2, and oneor more of the control device 300 of FIG. 3. Method 700 may include oneor more operations, functions, or actions as illustrated by one or moreof blocks 702-710. Although the blocks are illustrated in sequentialorder, these blocks may also be performed in parallel, and/or in adifferent order than those described herein. Also, the various blocksmay be combined into fewer blocks, divided into additional blocks,and/or removed based upon the desired implementation.

At block 702, the method 700 involves receiving, by a first playbackdevice, a first audio signal and a second audio signal. In one example,as discussed above in connection to the method 500, the first playbackdevice may be configured to play the first audio signal in synchronywith the playback of the second audio signal by a second playbackdevice. Accordingly, in one example, the first and second audio signalsmay be the audio signals 602 and 604, respectively shown and discussedin connection to FIG. 6A. In one example, the first and second playbackdevices may be playback devices 104 and 110, respectively shown inFIG. 1. In another example, the first and second audio signals may bethe audio signals 608 and 606 respectively shown and discussed inconnection to FIG. 6B, and the first and second playback devices may bethe playback devices 124 and 122, respectively shown in FIG. 1. Otherexamples are also possible.

At block 704, the method 700 involves the first playback devicedetermining a first limiting result by applying a first limitingfunction to the first audio signal. In this case, the first limitingfunction may be one that is associated with the first playback device,and may represent an acoustic limit of the first playback device. FIG.8A shows an example application of a limiting function 850 to the audiosignal 602 introduced previously in connection to the example of FIG.6A. In this example, the limiting function 850 may be the first limitingfunction associated with the first playback device, and as discussed inconnection to block 702, the audio signal 602 may be the first audiosignal to be played by the first playback device. Similar to therelevant discussions in connection to block 504 of the method 500,applying the limiting function 850 to the first audio signal 602 mayresult in a limited first audio signal 802′, which is a model of anaudio signal that may be rendered by the first playback device when thefirst playback device plays the first audio signal 602.

In this example, as shown in FIG. 8A, the limited first audio signal802′ and the first audio signal 602 may be the same because the signalvalue over the entire frequency range of the first audio signal 602 iswithin the acoustic limit of the first playback device as defined by thelimiting function 850. As such, the first limiting result determined byapplying the first limiting function 850 to the first audio signal 602may indicate that no scaling or reduction in gain to the first audiosignal 602 is necessary for the first playback device to properly playthe first audio signal 602.

At block 706, the method 700 involves the first playback devicedetermining a second limiting result by applying a second limitingfunction to the second audio signal. The second limiting function inthis example may be associated with the second playback device. As such,block 706 may be similar to block 504 of the method 500, and anydiscussions above in connection to block 504 may apply to block 706 aswell. For instance, the first playback device may be configured toreceive the second limiting function prior to determining the secondlimiting result. FIG. 8B shows an example application of a limitingfunction 860 to the audio signal 604 discussed previously in connectionto the example of FIG. 6A. In this example, the limiting function 860may be the second limiting function associated with the second playbackdevice, and as discussed in connection to block 702, the audio signal604 may be the second audio signal to be played by the second playbackdevice. Applying the limiting function 860 to the second audio signal604 may result in a limited second audio signal 804′, which is a modelof an audio signal that may be rendered by the second playback devicewhen the second playback device plays the second audio signal 604.

In this example, as shown in FIG. 8B, the limited second audio signal804′ is a proportionally scaled down version of the second audio signal604 such that the limited second audio signal 804′ is within theacoustic limit of the second playback device as defined by the limitingfunction 860. As shown in this illustrative example, the first limitingresult may indicate that the limited second audio signal 804′ is thesecond audio signal 604 scaled down by a ratio of f/(e+f).

At block 708, the method 700 involves the first playback devicedetermining a third limiting function based on the first limiting resultand the second limiting result. Similar to that discussed in connectionto block 506 of the method 500, one of the first and second audiosignals may be limited or proportionally scaled to match the limitedresult of the other for a balanced output between the playback of thefirst and second audio signals.

FIG. 8C shows each of the first audio signal 602, the limited firstaudio signal 802′, the second audio signal 604, and the limited secondaudio signal 804′. As discussed above, and as shown, applying the secondlimiting function 860 to the second audio signal 604 resulted in alimited second audio signal 804′ that was more limited than the limitedfirst audio signal 802′ that resulted from applying the first limitingfunction 850 to the first audio signal 602. Based on the first andsecond limiting results represented by the limited first audio signal802′ and the limited second audio signal 804′, respectively, a thirdlimiting function 870 may be determined such that an application of thethird limiting function 870 to the first audio signal 602 results in abalanced output between playback of the first audio signal 602 by thefirst playback device and playback of the second audio signal 604 by thesecond playback device. As shown, the limiting function 870, whenapplied, may be configured to scale the first audio signal 602 by aratio of j/(i+j) such that j/(i+j)=f/(e+f).

At block 710, the method 700 involves configuring the first playbackdevice to apply the third limiting function when playing the first audiosignal. Referring to FIG. 8D, the first playback device may beconfigured to apply the limiting function 870 to the first audio signal602 when playing the first audio signal. In one example as shown,application of the third limiting function 870 to the first audio signal802 may result in a limited first audio signal 812′ such that thelimited first audio signal 812′ is proportionally scaled down from thefirst audio signal 602 by the ratio of j/(i+j). As discussed above inconnection to block 508 of method 500, applying the limiting function870 to the first audio signal 602 may involve adjusting an amplifiergain applied to the first audio signal 602 by the first playback device.In one case, the amplifier gain may be adjusted to be j/(i+j) of unitygain. As also shown in FIG. 8D, the limited first audio signal 812′ andthe limited second audio signal 804′ are substantially as proportionallybalanced as the first audio signal 602 and second audio signal 604 shownin FIG. 6A. In one case, when configured to apply the third limitingfunction 670, the first playback device may effectively render thelimited first audio signal 612′ when playing the first audio signal 608.In another example, applying the third limiting function 870 to thefirst audio signal 802 may involve simply capping or clipping the firstaudio signal 602 according to the third limiting function 870, ratherthan proportionally scaling the first audio signal 602.

Synchronous playback of the first audio signal 802 with playback of thesecond audio signal 604 by the second playback device may be similar tothe synchronous playback of the first audio signal 608 by the firstplayback device and the second audio signal 606 by the second playbackdevice discussed previously in connection to the method 500 of FIG. 5.Along those lines, any previous discussions related to synchronousplayback of audio content by two or more playback devices may also beapplicable to method 700 and examples discussed in connection to themethod 700. Further, while discussions above relating to the method 700are generally directed to the balancing of audio output duringsynchronized playback by a consolidated player, one having ordinaryskill in the art will appreciate that method 700 may be applied to othersynchronized playback scenarios as well. In addition, note that in someembodiments, the illustrative examples discussed in connection to themethod 700 and FIG. 8A-8D represent only one instance of a dynamicbalancing of audio output during synchronized playback. In other words,method 700 may be performed for each data packet or series of datapackets containing audio signals received as part of a streaming audiocontent.

c. Third Example Method for Audio Output Balancing During SynchronizedPlayback

In the illustrative examples discussed above in connection to FIGS. 5and 7, determining a limiting function to be applied to the first audiosignal may generally be based on the acoustic limit of a playback devicein the stereo pair or consolidated player with the lowest acousticlimit. In other words, the limiting function may be determined such thatthe output of the first playback device when playing the first audiosignal is reduced to substantially match the output of the secondplayback device when playing the second audio signal if the synchronousplayback output of the two playback devices is increased beyond theacoustic limit of the second playback device. In the example discussedin connection to the method 700 and as shown in FIG. 8D, the resultingoutput volume of the rendered audio signal may be around 60 dB, which isover 20 dB less than the output volume of received audio signal of over80 dB. In some embodiments, depending on the acoustic limits andcapabilities of the first and second playback devices, the reduction inoutput volume may be reduced by dynamically adjusting a crossoverfrequency according to which the first playback device plays the firstaudio signal.

FIG. 9 shows a flow diagram of an example method 900 for adjusting acrossover frequency for audio output balancing during synchronizedplayback. Method 900 shown in FIG. 9 presents an embodiment of a methodthat can be implemented within an operating environment involving, forexample, the media playback system 100 of FIG. 1, one or more of theplayback device 200 of FIG. 2, and one or more of the control device 300of FIG. 3. Method 700 may include one or more operations, functions, oractions as illustrated by one or more of blocks 902-908. Although theblocks are illustrated in sequential order, these blocks may also beperformed in parallel, and/or in a different order than those describedherein. Also, the various blocks may be combined into fewer blocks,divided into additional blocks, and/or removed based upon the desiredimplementation.

At block 902, the method 900 involves receiving a first audio signal tobe played by a first playback device according to a first crossoverfrequency, and a second audio signal to be played by a second playbackdevice according to a second crossover frequency. Continuing with theexamples above, the first audio signal may be the audio signal 602 shownin FIG. 6A and the first crossover frequency may be the crossoverfrequency 610 of 80 Hz. Analogously, the second audio signal may be theaudio signal 604 and the second crossover frequency may also be thecrossover frequency 610 of 80 Hz. As indicated previously, in somecases, the first audio signal 602 and the second audio signal 604 may bedifferent components of an audio content.

In some embodiments, the first audio signal 602 and the second audiosignal 604 may be received individually, while in some otherembodiments, audio content including both the first audio signal 602 andthe second audio signal 604 may be received as a whole, and band-passfilters may be applied to the received audio content to generate thefirst audio signal 602 and the second audio signal 604. In some cases,the first and second crossover frequencies (in this example, both may bethe crossover frequency 610) may be received along with the audiocontent to generate and apply applicable band-pass filters. In someother cases, the first and second crossover frequencies may bepredetermined when the first and second playback devices were configuredas a consolidated player based on playback capabilities andconfigurations of the first and second playback devices. Block 902 maybe similar to block 702 discussed above in connection to FIG. 7.Accordingly, any relevant discussions in connection to the method 700 ofFIG. 7 may be applicable to block 902 as well.

At block 904, the method 900 involves determining a first limitingresult by applying a first limiting function to the first audio signal,and at block 906, the method 900 involves determining a second limitingresult by applying a second limiting function to the second audiosignal. Similar to blocks 704 and 706, respectively, and continuing withthe above examples, the first limiting function may be the limitingfunction 850 that is associated with the first playback device, and thesecond limiting function may be the limiting function 860 that isassociated with the second playback device, shown previously in FIGS. 8Aand 8B, respectively. As shown in FIG. 10A, the first limiting resultdetermined from applying the first limiting function 850 to the firstaudio signal 602 may include the limited first audio signal 802′, andthe second limiting result determined from applying the second limitingfunction 860 to the second audio signal 604 may include the limitedsecond audio signal 804′. As blocks 904 and 906 are similar to blocks704 and 706, respectively, any relevant discussions in connection to themethod 700 of FIG. 6 may be application to blocks 904 and 906 as well.

At block 908, the method 900 involves configuring the first playbackdevice to play the first audio signal according to a third crossoverfrequency. Configuring the first playback device to play the first audiosignal according to the third crossover frequency may involve firstdetermining the third crossover frequency. In one example, the thirdcrossover frequency may be determined based on the first limiting resultand the second limiting result. For instance, the third crossoverfrequency may be determined based on frequencies at which the secondplayback device is limited, and determining whether the first playbackdevice is capable of playing audio content in those frequencies. In theexample shown in FIG. 10A, the example third crossover frequency 1010may be determined to be the highest frequency at which the firstplayback device can render audio content of a satisfactory acousticquality and/or output volume. As suggested above, this may be the casewhen the second audio signal 604 was more limited by the limitingfunction 860 towards the lower end of the mid-high frequency range. Inthis example, the example third crossover frequency 1010 may be 150 Hz.

FIG. 10B shows an example first audio signal 1002 that may be played bythe first playback device according to the third crossover frequency1010 of 150 Hz. In this case, audio content including both the firstaudio signal 602 and the second audio signal 604 may be received by thefirst playback device. Subsequently, the first playback device may applyband-pass filters to the received audio content according to the thirdcrossover frequency 1010 to generate the first audio signal 1004 to beplayed by the first playback device. As indicated above, the firstplayback device may be configured to play the first audio signal 602 insynchrony with playback of the second audio signal 604. As such, thesecond playback device may be configured to play the second audio signal604 according to a fourth crossover frequency that may be determinedbased on the third crossover frequency and/or the first and secondlimiting results from blocks 904 and 906. FIG. 10B also shows an examplesecond audio signal 1004 that may be played by the second playbackdevice according to the fourth crossover frequency, which in thisexample may also be 150 Hz, same as the third crossover frequency 1010.

In one example, the first playback device may be configured to send tothe second playback device, data indicating the third crossoverfrequency, and configuring, or causing the second playback device to beconfigured to play the second audio signal according to the fourthcrossover frequency. In this case, the second playback device may beconfigured to determine the fourth crossover frequency based on thethird crossover frequency. In the case the second playback devicereceives the audio content including both the first audio signal 602 andthe second audio signal 604, the second playback device may beconfigured to apply band-pass filters according to the fourth crossoverfrequency to generate the second audio signal 1004 to be played by thesecond playback device. As indicated previously, the fourth crossoverfrequency may in some cases be the same as the third crossover frequency1010 of 150 Hz.

In another example, the first playback device may be configured todetermine the fourth crossover frequency based on the third crossoverfrequency, and send to the second playback device, data indicating thefourth crossover frequency. In this case the second playback device maybe configured to apply band-pass filters according to the fourthcrossover frequency 1010 to generate the second audio signal 1004 to beplayed without having to determine the fourth crossover frequencyitself.

Playback of the first audio signal 1002 by the first playback device insynchrony with playback of the second audio signal 1004 by the secondplayback device may result in a more balanced output than playback ofthe first audio signal 602 by the first playback device in synchronywith playback of the second audio signal 604 by the second playbackdevice. In some embodiments, the dynamic adjustment of crossoverfrequencies may result in sufficient audio output balancing duringsynchronized playback. In some other embodiments, however, additionalsteps, such as those described in connection to FIGS. 5 and 7 may beperformed to further balance audio output by the first and secondplayback devices during synchronous playback. For illustration purposes,FIGS. 10C-10E show an example application of the method 700 of FIG. 7 tothe first audio signal 1002 and the second audio signal 1004 of FIG.10B.

As shown in FIG. 10C, the first limiting function 850 may be applied tothe first audio signal 1002. In this example, the limiting result mayindicate that a limited first audio signal 1002′ generated from applyingthe first limiting function 850 to the first audio signal 1002 is thefirst audio signal 1002 scaled down by a ratio of n/(m+n). As shown inFIG. 10D, the second limiting function 860 may be applied to the secondaudio signal 1004. In this example, the limiting result may indicatethat a limited second audio signal 1004′ generated from applying thesecond limiting function 860 to the second audio signal 1004 is thesecond audio signal 1004 scaled down by a ratio of q/(p+q).

As indicated previously, one of the first audio signal 1002 and secondaudio signal 1004 may need to be limited or proportionally scaled tomatch the limited result of the other for a balanced output between theplayback of the first audio signal 1002 by the first playback device andplayback of the second audio signal 1004 by the second playback device.Comparing n/(m+n) and q/(p+q) as shown in FIGS. 10C and 10D, applyingthe second limiting function 860 to the second audio signal 1004resulted in a limited second audio signal 1004′ that was more limitedthan the limited first audio signal 1002′ that results from applying thefirst limiting function 850 to the first audio signal 1002. In otherwords q/(p+q) is less than n/(m+n) in this example.

Accordingly, as shown in FIG. 10E, a limiting function 1070 may bedetermined such that an application of the limiting function 1070 to thefirst audio signal 1002 results in a balanced output between playback ofthe first audio signal 1002 by the first playback device and playback ofthe second audio signal 1004 by the second playback device. As shown,the limiting function 1070, when applied, may be configured to scale thefirst audio signal 1002 by a ratio of y/(x+y) such that y/(x+y)=q/(p+q).

The first playback device may accordingly be configured to apply thelimiting function 1070 when playing the first audio signal 1002. Asshown, a limited first audio signal 1012′ generated when applying thelimiting function 1070 to the first audio signal 1002 is proportionallyscaled down from the first audio signal 1002 by the ratio of y/(x+y). Asindicated previously, applying the limiting function 1070 to the firstaudio signal 1002 may involve adjusting an amplifier gain applied to thefirst audio signal 1002 by the first playback device. As shown in FIG.10F, the limited first audio signal 1012′ and the limited second audiosignal 1004′ are substantially as proportionally balanced as the firstaudio signal 602 and second audio signal 602 shown in FIG. 6A. Asindicated previously, in some cases, applying the limiting function 1070to the first audio signal 1002 may involve simply capping or clippingthe first audio signal 1002 according to the limiting function 1070,rather than proportionally scaling the first audio signal 1002.

When compared to the limited first and second audio signals 812′ and804′ shown in FIG. 8D, the limited modified first and second audiosignals 1012′ and 1004′, as shown in FIG. 10F may be rendered at abalanced output volume of over 70 dB, which is less reduced from theoutput volume of 80 dB of the first and second audio signals 602 and 604than the balanced output volume of around 60 dB if rendering the limitedfirst and second audio signals 812′ and 804′.

While discussions above relating to the method 900 are generallydirected to the balancing of audio output during synchronized playbackby a consolidated player, one having ordinary skill in the art willappreciate that method 900 may be applied to other synchronized playbackscenarios as well. In addition, note that in some embodiments, theillustrative examples discussed in connection to the method 900 and FIG.10A-10F represent only one instance of a dynamic balancing of audiooutput during synchronized playback. In other words, method 900 may beperformed for each data packet or series of data packets containingaudio signals received as part of a streaming audio content. Otherexamples are also possible.

IV. Conclusion

The description above discloses, among other things, various examplesystems, methods, apparatus, and articles of manufacture including,among other components, firmware and/or software executed on hardware.It is understood that such examples are merely illustrative and shouldnot be considered as limiting. For example, it is contemplated that anyor all of the firmware, hardware, and/or software aspects or componentscan be embodied exclusively in hardware, exclusively in software,exclusively in firmware, or in any combination of hardware, software,and/or firmware. Accordingly, the examples provided are not the onlyway(s) to implement such systems, methods, apparatus, and/or articles ofmanufacture.

As indicated above, the present application involves balancing ofoutputs from playback devices playing audio content in synchrony. In oneaspect, a first playback device is provided. The first playback deviceincludes a processor, and memory having stored thereon instructionsexecutable by the processor to cause the first playback device toperform functions. The functions include receiving a first audio signal.The first playback device is configured to play the first audio signalaccording to a first crossover frequency. The functions also includedetermining a first limiting result by applying a limiting function to asecond audio signal. The second audio signal is configured for playbackby a second playback device according to a second crossover frequency,and the limiting function is associated with the second playback device.The functions further include, based on the first limiting result,configuring the first playback device to play the first audio signalaccording to a third crossover frequency.

In another aspect, a method is provided. The method involves receiving,by a first playback device, audio content comprising a first audiosignal and a second audio signal. The first playback device isconfigured to play the first audio signal according to a first crossoverfrequency in synchrony with the playback of the second audio signalaccording to a second crossover frequency by a second playback device.The method also involves determining a first limiting result byapplying, by the first playback device, a first limiting function to thefirst audio signal. The first limiting function is associated with thefirst playback device. The method further involves determining a secondlimiting result by applying, by the first playback device, a secondlimiting function to the second audio signal. The second limitingfunction is associated with the second playback device. The method alsoinvolves, based on the first limiting result and the second limitingresult, configuring the first playback device to play the first audiosignal according to a third crossover frequency.

In yet another aspect, a non-transitory computer readable memory isprovided. The non-transitory computer readable memory has stored thereoninstructions executable by a computing device to cause the computingdevice to perform functions. The functions include receiving a firstaudio signal. The first playback device is configured to play the firstaudio signal according to a first crossover frequency. The functionsalso include determining a first limiting result by applying a limitingfunction to a second audio signal. The second audio signal is configuredfor playback by a second playback device according to a second crossoverfrequency, and the limiting function is associated with the secondplayback device. The functions further include, based on the firstlimiting result, configuring the first playback device to play the firstaudio signal according to a third crossover frequency.

Additionally, references herein to “embodiment” means that a particularfeature, structure, or characteristic described in connection with theembodiment can be included in at least one example embodiment of aninvention. The appearances of this phrase in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments mutually exclusive of otherembodiments. As such, the embodiments described herein, explicitly andimplicitly understood by one skilled in the art, can be combined withother embodiments.

The specification is presented largely in terms of illustrativeenvironments, systems, procedures, steps, logic blocks, processing, andother symbolic representations that directly or indirectly resemble theoperations of data processing devices coupled to networks. These processdescriptions and representations are typically used by those skilled inthe art to most effectively convey the substance of their work to othersskilled in the art. Numerous specific details are set forth to provide athorough understanding of the present disclosure. However, it isunderstood to those skilled in the art that certain embodiments of thepresent disclosure can be practiced without certain, specific details.In other instances, well known methods, procedures, components, andcircuitry have not been described in detail to avoid unnecessarilyobscuring aspects of the embodiments. Accordingly, the scope of thepresent disclosure is defined by the appended claims rather than theforgoing description of embodiments.

When any of the appended claims are read to cover a purely softwareand/or firmware implementation, at least one of the elements in at leastone example is hereby expressly defined to include a tangible,non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on,storing the software and/or firmware.

We claim:
 1. A first playback device comprising: one or more processors;and computer-readable memory having stored thereon instructions that,when executed by the one or more processors, cause the first playbackdevice to perform functions comprising: receiving audio content to beplayed back by the first playback device and a second playback device insynchrony, wherein the audio content comprises a first stereo componentto be played by the first playback device and a second stereo componentto be played by the second playback device in synchrony with playback ofthe first stereo component by the first playback device; determining alimiting result that represents playback of the second stereo componentof the audio content by applying to the second stereo component of theaudio content, a pre-determined volume-limiting function that isassociated with the second playback device, wherein the limiting resultindicates frequencies at which a playback volume of the second playbackdevice is limited; determining a crossover frequency based on theindicated frequencies at which the playback volume of the secondplayback device is limited; causing the second playback device to play afirst portion of the second stereo component of the audio content thatis above the determined crossover frequency; and playing (i) the firststereo component of the audio content and (ii) a second portion of thesecond stereo component of the audio content that is below the indicatedfrequency in synchrony with playback of the first portion of the secondstereo component by the second playback device.
 2. The first playbackdevice of claim 1, wherein the first playback device has greater outputaudio frequency range than the first playback device.
 3. The firstplayback device of claim 1, wherein the functions further comprise:prior to receiving the audio content, receiving a command to form abonded zone with the second playback device.
 4. The first playbackdevice of claim 1, wherein the functions further comprise: identifying,in memory storage, the pre-determined volume-limiting function that isassociated with the second playback device.
 5. The first playback deviceof claim 1, wherein the functions further comprise: receiving, from thesecond playback device, the pre-determined volume-limiting function thatis associated with the second playback device.
 6. The first playbackdevice of claim 1, wherein causing the second playback device to playthe first portion of the second stereo component of the audio contentthat is above the determined crossover frequency comprises: sending tothe second playback device, the first portion of the second stereocomponent of the audio content.
 7. The first playback device of claim 1,wherein causing the second playback device to play the first portion ofthe second stereo component of the audio content that is above thedetermined crossover frequency comprises: sending, to the secondplayback device, (i) the audio content and (ii) a command to play thefirst portion of the second stereo component of the audio content. 8.The first playback device of claim 1, wherein causing the secondplayback device to play the first portion of the second stereo componentof the audio content that is above the determined crossover frequencycomprises: sending, to the second playback device, (i) the second stereocomponent of the audio content and (ii) a command to play the firstportion of the second stereo component.
 9. The first playback device ofclaim 1, wherein the determined crossover frequency is around 80 Hz. 10.Tangible, non-transitory computer-readable memory having stored thereoninstructions that, when executed by one or more processors of a firstplayback device, cause the first playback device to perform functionscomprising: receiving audio content to be played back by the firstplayback device and a second playback device in synchrony, wherein theaudio content comprises a first stereo component to be played by thefirst playback device and a second stereo component to be played by thesecond playback device in synchrony with playback of the first stereocomponent by the first playback device; determining a limiting resultthat represents playback of the second stereo component of the audiocontent by applying to the second stereo component of the audio content,a pre-determined volume-limiting function that is associated with thesecond playback device, wherein the limiting result indicatesfrequencies at which a playback volume of the second playback device islimited; determining a crossover frequency based on the indicatedfrequencies at which the playback volume of the second playback deviceis limited; causing the second playback device to play a first portionof the second stereo component of the audio content that is above thedetermined crossover frequency; and playing (i) the first stereocomponent of the audio content and (ii) a second portion of the secondstereo component of the audio content that is below the indicatedfrequency in synchrony with playback of the first portion of the secondstereo component by the second playback device.
 11. The tangible,non-transitory computer-readable memory of claim 10, wherein the firstplayback device has greater output audio frequency range than the firstplayback device.
 12. The tangible, non-transitory computer-readablememory of claim 10, wherein the functions further comprise: prior toreceiving the audio content, receiving a command to form a bonded zonewith the second playback device.
 13. The tangible, non-transitorycomputer-readable memory of claim 10, wherein the functions furthercomprise: identifying, in memory storage, the pre-determinedvolume-limiting function that is associated with the second playbackdevice.
 14. The tangible, non-transitory computer-readable memory ofclaim 10, wherein the functions further comprise: receiving, from thesecond playback device, the pre-determined volume-limiting function thatis associated with the second playback device.
 15. The tangible,non-transitory computer-readable memory of claim 10, wherein thedetermined crossover frequency is around 80 Hz.
 16. A method comprising:receiving, via a first playback device, audio content to be played backby the first playback device and a second playback device in synchrony,wherein the audio content comprises a first stereo component to beplayed by the first playback device and a second stereo component to beplayed by the second playback device in synchrony with playback of thefirst stereo component by the first playback device; determining, viathe first playback device, a limiting result that represents playback ofthe second stereo component of the audio content by applying to thesecond stereo component of the audio content, a pre-determinedvolume-limiting function that is associated with the second playbackdevice, wherein the limiting result indicates frequencies at which aplayback volume of the second playback device is limited; determining,via the first playback device, a crossover frequency based on theindicated frequencies at which the playback volume of the secondplayback device is limited; causing, via the first playback device, thesecond playback device to play a first portion of the second stereocomponent of the audio content that is above the determined crossoverfrequency; and playing, via the first playback device (i) the firststereo component of the audio content and (ii) a second portion of thesecond stereo component of the audio content that is below the indicatedfrequency in synchrony with playback of the first portion of the secondstereo component by the second playback device.
 17. The method of claim16, wherein the first playback device has greater output audio frequencyrange than the first playback device.
 18. The method of claim 16,wherein causing the second playback device to play the first portion ofthe second stereo component of the audio content that is above thedetermined crossover frequency comprises: sending, via the firstplayback device to the second playback device, the first portion of thesecond stereo component of the audio content.
 19. The method of claim16, wherein causing the second playback device to play the first portionof the second stereo component of the audio content that is above thedetermined crossover frequency comprises: sending, via the firstplayback device to the second playback device, (i) the audio content and(ii) a command to play the first portion of the second stereo componentof the audio content.
 20. The method of claim 16, wherein causing thesecond playback device to play the first portion of the second stereocomponent of the audio content that is above the determined crossoverfrequency comprises sending, via the first playback device to the secondplayback device, (i) the second stereo component of the audio contentand (ii) a command to play the first portion of the second stereocomponent.